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Novel Photon/Electron State For Efficient Lasers


Blue Lasers

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Richard Webb in NewScientist writes about a novel way of creating laser light, developing from an unusual mixture of electrons and photons. This technique could result in better amplifiers for communications, as well as very efficient lasers.

It starts pretty much the same way as normal semiconductor lasers do: a layer of trapped electrons are excited into a higher energy state, which emit photons when they fall back to normal. But the photons released are quickly reflected back to the electrons by polished mirrors about a micrometer away. The reflected photons excite more electrons, and the process begins anew.

The spacing of the mirrors create a resonance, with the photons creating excited electrons and electrons creating photons so quickly that quantum theory predicts that it is impossible to determine in what state is the system. This cloud of photons and electrons is called a polariton, or more specifically, an exciton–polariton, since the electrons are really part of an electron and hole pair (the hole being where the electron left when it became excited) known as an exciton.

In a normal semiconductor laser, the electrons won’t occupy the same quantum state without a lot energy put into the system. But polaritons do this easily, requiring much less energy to get going. This energy can be supplied by a voltage, or by photons from an outside source.

Researchers from universities of Sheffield and Southampton, both in the UK, showed in 2000 that laser light shone into such a system could be amplified by close to 100 times, a remarkable feat. But it has proven difficult to reproduce this with materials that work at room temperature. Also difficult is to producing a lasing effect using electrical pumping of the material. Work at the University of Crete in February 2009, however, has resulted in a room–temperature polariton–based LED that is electrically driven. These LEDs could prove to be more efficient than normal LEDs.

Webb’s article goes on to describe how these polaritons could also be used as logic circuits themselves, while creating the light needed for rapid communications between components in a computer system. Even further, there is the possibility that they could be used for quantum computers.



April 8, 2009 - Posted by | Uncategorized

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